Fragile articles such as the above-mentioned precious artistic work, left in a cabinet, a whatnot, or a showcase, are prone to tumble or fall down to fracture because of a shake by an earthquake. Usually, the articles are guarded by strained rope or bracing that surrounds the articles. As to a particularly large artwork showpiece, several strings of rope are typically strained and separated by a certain distance from each other. However, such manners are unsatisfactory as a full protection means from articles' tumbling or falling down. They also give esthetically adverse effects as well as bothering obstacles to viewers.
In order to overcome the aforementioned disadvantages, there has been developed an earthquake-proof plinth that comprises a holder supporting a showpiece seated thereon, a sensor for detecting vibration, a releaser receiving a signal from the sensor for making the holder release the showpiece, and a protecting means located under the holder to serve as a drop and shelter to receive and protect the showpiece released from the holder where the releaser includes a solenoid device activated by the signal from the sensor and a stopper disengaged from the holder by means of the solenoid device (see Patent Document 1 listed below).
Another type of the plinth has been disclosed which comprises a base of a certain height with a pair of apertures opposed to each other in the top and bottom plates of the base where the aperture in the top plate can be opened and closed by sliding a pair of shutters that meet each other at the center of the aperture while the bottom plate is skirted around the aperture by a shock-absorbing and volume-adjustable sac with its upper open end fixed to bottom plate so that the sac hangs down and is ready for trap an artistic showpiece fallen from its seated location. This type of the plinths further comprise an actuating device and a vibration sensor, and the vibration sensor detects vibration caused by an earthquake and makes the actuating device move the shutters to leave the aperture open, so as to protect the artistic showpiece from liable damages (see Patent Document 2 listed below).
Still another type of the plinth has an aperture formed in a level flush with a surface of a showpiece mount to follow contours of the middle portion of a showpiece seated thereon, and the plinth comprises a base plate capable of passing vertically through the aperture and supported by a shaft extending vertically downward therefrom, a vibration sensor, a stopper means for shock-absorbingly stopping the base-plate supporting shaft when the showpiece drops till its middle portion becomes fitted in to choke up the aperture in the plinth, and a lock/unlock means for normally locking the base-plate supporting shaft to keep the base plate flush with the surface of the showpiece mount and unlocking the base-plate supporting shaft upon receiving a detection signal from the vibration sensor to let the base-plate supporting shaft drop along with the base plate (see Patent Document 3 listed below).    Patent Document 1: Japanese Patent No. 2746253    Patent Document 2: Japanese Patent No. 3458089    Patent Document 3: Japanese Patent Preliminary Publication No. 2007-222481
In the earthquake-proof plinths as disclosed in Patent Document 1, when the showpiece is released from the holder and gravitationally dropped into the trap with shock-absorbing material such as sponge, the showpiece received at the bottom of the trap is prone to make a large bumping noise or even be damaged. Also, this type of the prior art plinth is not capable of keeping showpiece mount without a tilt, and therefore, the showpiece is prone to have its finished surface, edges, and/or flourishes chipped or cracked upon being gravitationally dropped.
In the earthquake-proof plinth as disclosed in Patent Document 2, the elastic sac is an essential component, and the actuating device for the shutters is complicated in structure. In addition, this type of the prior art plinth encounters difficulties that a showpiece cannot be kept without a tilt on exhibit and that vertical dimensions of the plinth cannot be reduced.
In the prior art plinth as disclosed in Patent Document 3, since the base plate is supported by the shaft, it is hard to keep the showpiece horizontal on exhibit, and it is also hard to reduce vertical dimensions of the plinth. In addition, this type of plinth inevitably has an actuating device complicated in structure.
Accordingly, it is an object of the present invention to provide an earthquake-proof plinth adapted to make a showpiece seated thereon vertically go down instantaneously at the onset of an earthquake so as to buffer impact on the entire showpiece.
It is another object of the present invention to provide an earthquake-proof plinth that is adapted to keep the showpiece seated thereon upright without a tilt and that can ensure a full protection of the showpiece in response to a shake due to an earthquake or the like so as to avoid its tumbling down and being damaged.
It is still another object of the present invention to provide an improved plinth that is compact, easy to install, and reduced in manufacturing cost.